remove TimeIotaMs from ABCI consensus params (#3403)

Also

- init substructures to avoid panic in pb2tm.ConsensusParams
Before: if csp.Block is nil and we later try to access/write to it,
we'll panic.
After: if csp.Block is nil and we later try to access/write to it,
there'll be no panic.

docs/spec/abci/abci.md

@@ -456,8 +456,6 @@ Commit are included in the header of the next block.
     - NOTE: blocks that violate this may be committed if there are Byzantine proposers.
         It's the application's responsibility to handle this when processing a
         block!
-  - `TimeIotaMs (int64)`: Minimum time increment between consecutive blocks (in milliseconds).
-
 
 ### EvidenceParams